Pressure monitor optimizaiton of fluid path utilization

ABSTRACT

A device comprising a pressure monitor and a control means that receives a signal representing measured pressure at the pressure monitor and controls the controllable elements of a fluid system is utilized to monitor a fluid system for error conditions, to optimize operations and to diagnose the fluid system. By following a testing protocol that selectively enables parts of the system, the control means narrows the list of possible failing components. Comparing the measured pressure against normal pressures allows the device to identify error conditions. Determining the volume of fluid being transported and controlling the duration of the flow optimizes operation of the fluid system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/416,364, filed Mar. 9, 2012, which is a continuation of U.S.application Ser. No. 10/598,075, filed Jun. 11, 2008, which is theNational Stage of International Application No. PCT/US2005/006673 filedon Mar. 2, 2005, which claims priority to and benefit of U.S.Provisional Patent Application No. 60/550,415, filed Mar. 5, 2004. Thecontents of these applications are incorporated herein by reference.

STATEMENT ON FEDERALLY SPONSORED RESEARCH

N/A

FIELD OF THE INVENTION

The present invention relates to fluid movement systems and inparticular to improved operation and maintenance of such systemsutilizing a pressure monitor.

BACKGROUND OF THE INVENTION

In one form of liquid chromatography sample injection, the fluid pathfor handling the sample is pressurized. Such pressurization improves thesample movement speed by limiting the risk of vaporization of thesample. In order to control the degree of pressurization in such asystem, a pressure gauge is typically installed in line with thepressure source. This pressure gauge is typically used in a feedbackmode to control the generated pressure.

The increased pressure increases the likelihood of leakage at each ofthe multiple connection points that comprise the fluid path(s). Leaksmay occur due to wear internal to a component, when a component isreplaced due to faulty installation and also due to failures in jointsat unexpected areas. For fluid movement systems that have smalldiameters, the volume of fluid leaking may be large enough to distortperformance and yet small enough that it evaporates or is in some otherway rendered invisible to inspection.

A system controller can use the output of the pressure gauge to tellthat there is fluid leakage in the system when there is a greater thannormal pressure drop in the system. However, this technique does nothelp to isolate the source of the leak. Certain techniques may limit thesearch area for the leak rather than eliminate leak target areas.

Previous systems have been able to determine that there is a leak in thesystem, but have not been able to identify the location of the leak noridentify points without leaks. Therefore, repair operations havetypically involved disconnecting all connections, replacing many activecomponents and essentially rebuilding the fluid movement system when aleak became too severe. Because of the extent of the repair activities,lesser leaks were allowed to remain until the system could be broughtdown for the major replacement operation.

Many pressurized injection systems require a cleaning cycle betweensuccessive usage cycles. In order to assure adequate cleaning, a setvolume of cleaning fluid must pass through the system. In order tolessen the need for user interaction, the systems are set up for theextremes of operation. Since viscous liquids will take longer to flowthrough the system in a cleaning cycle, sufficient time is allocated forthe most viscous fluid anticipated to execute the cleaning cycle. Forall other fluids, some part of this time is wasted. If the viscosity ofthe fluid were known, the operation of the cleaning cycle could betailored to optimize the fluid path cleaning cycle.

Diagnostics for fluid systems would allow inefficient and/or failingcomponents to be identified. One set of information available is theexpected pressure and pressure decay within a fluid system. If theactual pressures experienced by the system can be measured, comparisonscan be conducted against the expected values.

Repairing a leak involves first finding it. Identifying the leakagepoint is beneficial because the repair time is minimized. Another timewhen checking for leaks is important is when a component is replaced andreconnected with the fluid system.

SUMMARY OF THE INVENTION

A device for monitoring pressure in a fluid system comprises a pressuremonitor for placement in communication with a fluid in the fluid systemand a control means for receiving a signal representative of themeasured pressure and comparing that measured pressure to a reference.The pressure monitor generates the signal representative of the measuredpressure and the control means generates an error message or performs anaction if a difference between the measured pressure and the referenceexceeds a predetermined value. One fluid system well adapted to thismonitoring is an autosampler for a liquid chromatography system.

In one embodiment, a fluid system is comprised of a controllablepressure source, at least one fluid path section having first and secondends and at least one fluid connection means. The fluid system is filledwith fluid and monitored by the device for monitoring pressure. Thecontrollable pressure source creates a source pressure on the fluid inresponse to a pressure command signal from the control means. The fluidconnection means has a plurality of ports for interconnection with thesystem and is capable of assuming a first position where fluid flowsbetween at least a first port and the second port and a second positionin which fluid does not flow between any of the first ports and thesecond port. The system is interconnected with one port of the fluidconnection means connected to an end of the fluid path section and thecontrollable pressure sources connected to the second end of the fluidpath section. The fluid connection means is responsive to a connectcommand signal to assume the first position and a disconnect commandsignal to assume the second position. The monitoring device is placed incommunication with the fluid in the fluid path section. The monitoringdevice sends the signal representing the measured pressure to thecontrol device for comparison with the known source pressure. Thecontrol means generates an error message if a difference between themeasured pressure and the source pressure exceeds a predetermined value.

In a preferred embodiment, the control means is further for sending aconnect command signal and a disconnect command signal to the at leastone fluid connection means for controlling the connection means toassume the first and second positions. In addition, the control means isfurther for sending a pressure command signal to the controllablepressure source to cause the controllable pressure source to generate asource pressure.

Preferably, the fluid system has one of the fluid connection means inthe second position, creating a closed fluid system. Then the controlmeans monitors the measured pressure in the closed fluid system overtime to detect a degradation of the measured pressure, which isindicative of a lack of fluid sealing integrity.

Preferably, the controllable pressure source is a syringe, preferably ametering syringe, positionable by the pressure command signals to createthe source pressure on the fluid. Further, at least one fluid connectionmeans is preferably a multiport valve having at least a first port and asecond port. In the first position, fluid flows between the first portand the second port. In a preferred embodiment, the fluid system is aliquid chromatography system and more particularly, a liquidchromatography sample injector system. In operation, the control meanssends a pressure command signal to the controllable pressure source tocreate a predetermined source pressure and reports an error if themeasured pressure does not reach a predetermined value within aspecified period of time.

In a preferred embodiment, the control means has a library of entriesthat comprise command signals to be sent, time between sending thecommand signals and taking readings and normal measured pressure values.The control means transmits the command signals for one entry andcompares a set of received measured pressures to the normal measuredpressure values. Differences that exceed a preset threshold cause areport to be sent.

In one embodiment, a fluid system that is to be monitored for errors iscomprised of a monitored fluid path section having a first end and asecond end and first and second fluid subsystems connected to the firstand second ends respectively. Each fluid subsystem comprises at leastone fluid path section, at least one fluid connection means and at leastone controllable pressure source. The fluid path sections in the fluidsubsystems have a section first end and a section second end. The fluidconnection means have a plurality of ports for interconnection. At leastone of the ports is connected to a fluid path section end for formingthe fluid subsystem. The fluid connection means are responsive to aconnect command signal to assume a first position wherein fluid flowsbetween at least two of the ports and responsive to a disconnect commandsignal to assume a second position in which fluid does not flow betweenany of the plurality of ports. The controllable pressure source isconnectable to the at least one section second end. The controllablepressure source is responsive to a pressure command signal to create asource pressure on fluid in the fluid subsystem. The first fluidsubsystem is connected to the first end of the monitored fluid pathsection and the second fluid subsystem is connected to the second end ofthe monitored fluid path section. The pressure monitor is incommunication with the monitored fluid path section. The control meanslooks for leakage in the system by monitoring the measured pressure overtime, looking for a degradation that would be indicative of a leak.

The control means controls the pressure and configuration of the fluidsystem while monitoring the measured pressure. The control meansexecutes a set of instructions that specify connect and disconnectcommand signals that define a configuration and pressure command signalsfor setting the source pressure. The instructions further specify thenormal measured pressure for each entry so that actual measured pressurecan be compared to the normal pressure. Degradations in the monitoredmeasured pressure are indicative of reduced fluid integrity of the fluidsystem configuration.

When trying to find leaks, the control means issues at least one connectcommand signal and at least one disconnect command signal to form afirst closed fluid circuit in the fluid system. The control means thenpressurizes the first closed fluid circuit using the controllablepressure source and monitors the pressure. If the pressure becomesestablished in the circuit and remains stable, the control meansconcludes that the components and interconnections making up the firstclosed fluid circuit likely are not leaking. The control means can thenexpand the length of subsequent closed fluid circuits and incrementallyadd to the list of non-leaking components and interconnections. Itshould be understood that each of the fluid connection means can becomposed of an interconnection of fluid connection means.

When the monitoring device can control the configuration of the fluidsystem by selectively isolating pans of the fluid system from the restusing the fluid connection means, successive fluidic integrity tests ondifferent parts of the fluid system lead to isolation of a leakingcomponent. By starting with a subsystem of the fluid system with fewcomponents, and verifying that there are no leaks in that part, thecontrol means has a basis for comparison as further components areadded. Each successive subsystem incorporates some previously testedcomponents and some untested parts, allowing the control means toidentify likely leaking components.

The device is preferably used to determine a parameter of a fluid in thefluid system. The control means that has been provided with referenceinformation based on the diameters of the fluid path components, thelength of a reference flow path and the friction factor of the referenceflow path, can use that information with the measured pressure of thefluid moving past the monitor point at a known flow rate to determinethe viscosity of the fluid. The viscosity can further be used tocalculate the flow rate that can be used in the wash cycle withoutexceeding a predetermined parameter of the system.

Preferably, the device is used with fluid system to optimize a fluidpath wash cycle. In an embodiment of a fluid path wash cycle using thedevice, one controllable pressure source comprises a first wash syringecontaining a first wash fluid. A first fluid connection means is used toconnect the first wash syringe to the fluid path to be flushed. Aftersending connect and disconnect command signals to the necessary fluidconnection means for configuring the system for flushing, includingcreating the fluid path to be flushed, the control means connects thefirst wash syringe through the appropriate connection means. The controlmeans monitors the measured pressure as the first wash syringe startsdelivering wash fluid. When the measured pressure equals a first washpressure that was calculated based on the viscosity of the fluid, thecontrol means stabilizes the flow rate of fluid being delivered.Thereafter, the control means allows the precise volume of wash fluidneeded to effect a complete wash to flow through the system in a timelymanner. This washing mechanism saves time over systems that flow washfluid based on a worst case viscosity. For systems that require twolevels of washing, the controllable pressure source comprises a firstand a second wash syringe filled respectively with a first wash fluidand a second wash fluid. Further the connection means is able to selectbetween the first and second wash syringes. After washing with the firstfluid, the control means repeats the process with the second washsyringe until a predetermined volume of second wash fluid has beenpushed through the fluid system to be cleaned.

Methods of performing operations on a fluid system are built around thedevice for measuring pressure. In a method of monitoring pressure, thefluid system is comprised of at least one fluid path section having afirst end and a second end and at least one controllable pressure sourceconnected to the first end of the at least one fluid path section. Eachcontrollable pressure source is responsive to a pressure command signalto create a source pressure in the at least one fluid path section. Thefluid system is connected so that it forms a fluid path filled with afluid. The method comprises providing the device comprising a pressuremonitor for placement in communication with the fluid in a first pathsection and a control means. The pressure monitor generates a signalrepresentative of a measured pressure that is received by the controlmeans. The control means sends signals to the fluid system. The pressuremonitor is placed in communication with the fluid in the fluid path. Thecontrol means issues a pressure command signal to the controllablepressure source to cause it to generate the source pressure in one fluidpath section. The control means compares the measured pressure to thesource pressure, and generates an error message if the differencebetween the measured pressure and the source pressure exceeds apredetermined value.

Preferably, the method determines whether the pressure in a pressurizedsystem is established within a specified time after a source pressure isapplied. In addition, a method to determines whether a decay in thepressure falls within prescribed limits. The fluid system furthercomprises at least one fluid connection means having a plurality ofports for interconnecting with the at least one controllable pressuresource and the at least one fluid path section. The fluid connectionmeans is capable of assuming at least a first position wherein fluidflows between at least two of the plurality of ports in response to aconnect command signal and a second position in which no fluid flows inresponse to a disconnect command signal. A preferred fluid connectionmeans is a multipart valve.

A preferred system comprises a first fluid connection means having atleast a first port and a second port, a second fluid connection meanshaving at least a first port and a second port, a first fluid pathsection and at least one controllable pressure source. A controllablepressure source is connected to the first port of the first fluidconnection means and the second port of the first fluid connection meansis connected to a first end of the first fluid path section. The secondend of the first fluid path section is connected to the first port of asecond connection means. The method further comprises sending at leastone connect command signal to the first fluid connection means to placethe first connection means in the first, open position. And sending atleast one disconnect command signal to the second fluid connection meansto place the second fluid connection means in the second, closed,position. This arrangement of fluid connection means creates a closedsystem that should maintain an applied pressure. The control means sendsa pressure command signal to the controllable pressure source togenerate a predetermined source pressure. The control means compares themeasured pressure to the predetermined source pressure and reports anestablishment error if the difference is greater than a first allowedamount. If no establishment error occurs, the method preferably furtherwaits a predetermined length of time and compares the current measuredpressure to the predetermined source pressure. If the decay in pressureis greater than a second allowed amount, a leak error is reported.

The method above is preferably extended to deal with more complex fluidsystems. The control means is provided with a library of entriescomprising sets of command signals for controlling connection means andpressure sources and sets of normal pressure values and allowablepressure decay rates. The control means selects one entry, issues thecommand signals from that entry and compares the measured pressures tothe normal pressure values. The control means reports significantdifferences. Preferably, the method has the control means issue connect,disconnect and pressure command signals to the fluid system and identifydegradations in the measured pressure indicative of reduced fluidintegrity.

The method is adaptable to other configurations. For instance, when asecond controllable pressure source is connected to the second port ofthe second fluid connection means, the method has further steps. Thecontrol means sends at least one connect command signal and disconnectcommand signal to the first and second fluid connection means to placethe first fluid connection means in the second position and the secondfluid connection means in a different first position where fluid flowsbetween the first fluid path and the second controllable pressuresource. The control means sends at least one pressure command signal tothe second controllable pressure source to set the source pressure. Thecontrol means monitors the signal from the pressure monitor andidentifies additional non-leaking components based on the stability ofthe measured pressure over time. When a third controllable pressuresource is connected to a third port of the second fluid connectionmeans, the method is extended similarly to identify further non-leakingcomponents.

The method is applicable and provides additional information when anadditional controllable pressure source is located at a different fluidconnection means in the fluid circuit. In particular, when a secondcontrollable pressure source is connected to a second port of the firstfluid connection means, the control means interconnects the fluidcircuit by sending connect command signals to the first fluid connectionmeans to assume a first position in which fluid flows between the firstfluid path and the second controllable pressure source. In addition, thecontrol means sends disconnect command signals to the second fluidconnection means to assume a second position blocking the fluid path.Then the control means sends a pressure command signal to the secondcontrollable pressure source to pressurize the fluid path. By monitoringthe signal from the pressure monitor, the control means identifiesadditional non-leaking components based on the stability of the measuredpressure over time. Preferably, the first fluid connection meanscomprises an interconnection of a plurality of fluid connection meansand the second fluid connection means comprises an interconnection of aplurality of fluid connection means.

BRIEF DESCRIPTION OF THE DRAWINGS

The above noted and other features of the invention will be betterunderstood from the following detailed description, when considered inconnection with the accompanying drawings, in which:

FIG. 1 is a schematic of an implementation of the inventive device;

FIG. 2A is a schematic of the device of FIG. 1 in a fluid system;

FIG. 2B is an illustration of the fluid system of FIG. 2A with commandsignals connected to components of the fluid system;

FIG. 3 is an illustration of a fluid system comprising two connectedfluid subsystems being monitored by the device of FIG. 1;

FIG. 4 is an illustration of the device of FIG. 1 being used to optimizea fluid system wash cycle;

FIGS. 5A and 5B illustrate a sequence of tests based on the fluid systemof FIG. 3, wherein FIG. 5A illustrates a first configuration and FIG. 5Billustrates a second configuration;

FIG. 6A illustrates a first test configuration of an example;

FIG. 6B illustrates a second test configuration of an example;

FIG. 6C illustrates a third test configuration of an example;

FIG. 6D illustrates a fourth test configuration of an example; and

FIG. 6E illustrates the failures identified by the tests of FIGS. 6A-6D.

DETAILED DESCRIPTION

As used herein, the term “leak” refers to a hole, crack or openingthrough which fluid escapes in a manner not intended by the user. Theleak may be totally internal. That is, the fluid escapes from an area ofhigh pressure to an area of low pressure within the apparatus. Or, suchleak may be external, allowing fluid to escape from the confines of thehydraulic circuit. Leaking fluids could represent a safety concern, thedetection of which would be very useful.

As used herein, “pressure monitor” comprises any device for measuringpressure, including strain gauges and pressure transducers. The outputof the pressure monitor, representing a measured pressure, may be ananalog signal that is digitized before being input to a control means ormay be a digitized representation of the measured pressure.

Fluid connection means are devices for closing, opening or directingfluid flow. In many cases a fluid connection means is a valve. Typicalvalves include mechanical check valves and active valves. Mechanicalcheck valves are responsive to pressure. Active valves receive a signalthat directs power means, such as motors, solenoids and the like, toopen or close the valve. Cycling valves are capable of selectivelyopening and closing the flow of fluid from one or more sources ordirecting the flow to one or more destinations.

As used herein, the term “control means” means any processing entitythat can receive information signals and send command signals. Anembedded microprocessor with memory and an associated input/outputsection for signal handling is one implementation. Alternately, one ofthe central processors embedded in an instrument may act as the controlmeans with the memory and input/output sections handling the instrumentas well as the device functions. Other central processors, as are knownto those skilled in the art, can serve as the control means.

A controllable pressure source is a device that can be commanded toexert a defined pressure on a fluid. Such a pressure source mayestablish a pressure in a closed fluid system. Alternately, the appliedpressure will cause a flow rate in an open fluid system. One example ofa controllable pressure source is a metering syringe wherein a motor isused to drive the syringe precisely.

As illustrated in FIG. 1, a device 10 for monitoring pressure in a fluidsystem 18 comprises a pressure monitor 12 for placement in communicationwith a fluid 16 in the fluid system 18 and a control means 14 forreceiving a signal 20 representative of the measured pressure andcomparing that measured pressure to a reference. The pressure monitor 12generates the signal 20 representative of the measured pressure and thecontrol means 14 generates an error message, and/or other signals 22 ifa difference between the measured pressure and the reference exceeds apredetermined value. One fluid system well adapted to this monitoring isa an auto sampler for a liquid chromatography system.

Turning now to FIG. 2A, a fluid system 18 is comprised of a controllablepressure source 30, at least one fluid path section 32 having first andsecond ends 34, 36 and at least one fluid connection means 40. The fluidsystem is filled with fluid 16 and monitored by the device 10 formonitoring pressure. The controllable pressure source 30 creates asource pressure on the fluid 16 in response to a pressure command signal38 from the control means 14. The fluid connection means 40 has aplurality of ports 42, 44, 46, 48 for interconnection with the systemand is capable of assuming a first position (represented by the dottedline 50) where fluid flows between a first port 44, 46 48 and the secondport 42 and a second position (not illustrated) in which fluid does notflow between any of the first ports 44, 46, 48 and the second port 42.The system 18 is interconnected with one port 42 of the fluid connectionmeans 40 connected to an end 34 of the fluid path section 32 and thecontrollable pressure source 30 connected to the second end 36 of thefluid path section 32. The fluid connection means 40 is responsive to aconnect command signal 52 to assume the first position and a disconnectcommand signal 54 to assume the second position. These signals may beimplemented as separate levels on one signal line, encodings on a line,distinct signals or other means including a combination of the aboveimplementations as is known to one skilled in the relevant art. Themonitoring device 12 is placed in communication with the fluid 16 in thefluid path section 32 and sends the measured pressure signal 20 forcomparing the measured pressure to the source pressure. The controlmeans 14 does the comparison and generates an error message 22 if adifference between the measured pressure and the source pressure exceedsa predetermined value.

As illustrated in FIG. 2B, the control means 14 is further for sendingthe connect command signal 52 and disconnect command signal 54 to the atleast one fluid connection means 40 for controlling the connection means40 to assume the first and second positions. In addition, the controlmeans 14 is further for sending the pressure command signal 38 to thecontrollable pressure source 30 to cause the controllable pressuresource 30 to generate the source pressure.

In an embodiment for testing for leakage, the fluid system has one ofthe at least one fluid connection means 40 in the second position,blocking fluid passage and creating a closed fluid system. Then, thecontrol means 14 can monitor the measured pressure in the closed fluidsystem over time to detect a degradation of the measured pressure, whichis indicative of a lack of fluid integrity.

Preferably, the controllable pressure source 30 is a syringe, preferablya metering syringe, positionable by the pressure command signal 38 tocreate the source pressure on the fluid 16. Further, the at least onefluid connection means 40 is preferably a multiport valve having atleast a first port and a second port. In the first position, fluid flowsbetween the ports, and in the second position fluid does not flowbetween any of the ports. When the multiport valve has more than twoports, there may be more than one first position in that in a firstfirst position fluid flows between ports A and B, while in a secondfirst position fluid may flow between ports A and C (or C and D). In apreferred embodiment, the fluid system is a liquid chromatography systemand more particularly, a liquid chromatography sample injector system.In operation, the control means 14 sends a pressure command signal 38 tothe controllable pressure source 30 to create a predetermined sourcepressure and reports an error if the measured pressure does not reach apredetermined value within a specified period of time.

In a preferred embodiment, the control means 14 has a library of entriesthat comprise command signals 38, 52, 54 to be sent, time and normalmeasured pressure values. The control means 14 transmits the commandsignals 38, 52, 54 to specified fluid connection means and controllablepressure sources for one entry and compares received measured pressuresto the normal measured pressure values. Differences that exceed a presetthreshold cause a report to be sent.

In one embodiment illustrated in FIG. 3, a fluid system that is to bemonitored for errors is comprised of a monitored fluid path section 60having a first end 62 and a second end 64 and first and second fluidsubsystems 70, 72 connected to the first and second ends 62, 64respectively. Each fluid subsystem 70, 72 comprises at least one fluidpath section 32, 32′, at least one fluid connection means 40, 40′, 40″,40′″ and at least one controllable pressure source 30, 30′, 30″, 30′″.The fluid path sections 32, 32′ have a section first end 34, 34′ and asection second end 36, 36′. The fluid connection means 40, 40′, 40″,40′″ have a plurality of ports, for instance ports 41′, 43′ and 45′ offluid connection means 40′. These ports are for interconnecting thesystem. At least one of the ports 41′ is connected to a fluid pathsection end 36 for forming the fluid subsystem. The fluid connectionmeans 40, 40′, 40″, 40′″ are responsive to connect command signals 52,52′, 52″, 52′″ respectively to assume a first position wherein fluidflows between at least two of the ports and responsive to disconnectcommand signals 54, 54′, 54″, 54′″ respectively to assume a secondposition in which fluid does not flow between any of the plurality ofports. As illustrated in FIG. 3, each illustrated fluid connection meanshas three possible first positions—using fluid connection means 40 forexample, connecting ports 41 and 43, 41 and 45 or 43 and 45 as well thesingle second position wherein no fluid flows. A controllable pressuresource 30, 30′, 30″, 30′″ may be connected to the at least one sectionsecond end 34 directly (not shown) or through a fluid connection means.The controllable pressure sources 30, 30′, 30″, 30′″ are responsive topressure command signals 38, 38′, 38″, 38′″ respectively to create asource pressure on fluid in the fluid subsystem. In the figure, each ofthe controllable pressure sources in connected to an end of the fluidpath section 32, 32′ and/or to the monitored fluid path 60 through atleast one connection means. The first fluid subsystem 70 is connected tothe first end 62 of the monitored fluid path section 60 and the secondfluid subsystem 72 connected to the second end 64 of the monitored fluidpath section 60. The pressure monitor 14 is in communication with themonitored fluid path section 60.

The control means 14 controls the pressure and configuration of thefluid system while monitoring the measured pressure. The control meansexecutes a set of instructions that specify connect and disconnectcommand signals to be sent to define a configuration and pressurecommand signals for setting the source pressure. The instructionsfurther specify the normal measured pressure for each entry, so that theactual measured pressure can be compared to the normal pressure.Degradations in the monitored measured pressure are indicative ofreduced fluid integrity of the fluid system configuration.

As an illustration, the control means 14 sends connect and disconnectcommand signals to the subsystems to create a configuration with oneconnection means 40′ in one subsystem 70 in the second position (closed)and a second connection means 40″ in the other subsystem 72, in thefirst position (open) so that the fluid is in a closed system comprisedof the controllable pressure source 30″, connection means 40, andmonitored fluid path 60 and the termination at fluid connection means40′. Then the control means 14 sends a pressure command signal 38″ toset the source pressure to a value. By monitoring the signal 20 from thepressure monitor 12 and noting whether the measured pressure remainsstable over time, the control means 14 is able to identify non-leakingcomponents.

When the monitoring device 10 can control the configuration of the fluidsystem by selectively isolating parts of the fluid system from the restusing the fluid connection means, successive fluidic integrity tests ondifferent parts of the fluid system lead to isolation of the leakingcomponent. By starting with a subsystem of the fluid system with fewcomponents, and verifying that there are no leaks in that part, thecontrol means 14 has a basis for comparison as further components areadded. Each successive subsystem incorporates some previously testedcomponents and some untested parts, allowing the control means toidentify likely leaking components.

The device is further preferably used to determine the viscosity of thefluid currently in the fluid system. Prior to this operation, the fluidsystem is calibrated to yield a viscosity calibration factor.Thereafter, when a fluid is flowed through the calibrated fluid path ata predetermined flow rate, the viscosity of the current fluid can bedetermined by multiplying the measured pressure by the viscositycalibration factor. In calibrating the fluid system, using equation (1)is used.η=VΔPD _(Ref) ⁶/64CL _(ref) Q ²  (1)In equation (1), ΔP is the difference from source pressure at themeasurement point, and, V, D_(ref), C, L_(ref) and Q are incorporated ina the viscosity calibration factor from the calibration run. (V isvelocity, D_(ref) is the average diameter of the reference fluid path, Cis a unit correcting factor, L_(ref) is the length of the referencefluid path, and Q is the flow rate used in the calibration run andmeasurement run).

Preferably, the device 10 is further used with a fluid system tooptimize a fluid path wash cycle. Using the configuration of componentsin FIG. 4, the fluid path to be washed 62 extends from fluid pathsection 84 to the fluid connection means 40″ that connects thecontrollable pressure source 30″, wherein here, the controllablepressure source 30″ is a first wash syringe containing a first washfluid. The control means 14 executes a series of instructions that causethe control means 14 to send connect command signals 52, 52′, 52″ tofluid connection means 40, 40′, 40″ to interconnect the fluid path 62 asillustrated for flushing. The control means 14 may send disconnectcommand signals 54 to other fluid connections means (not shown) toeliminate fluid path sections that are not be washed. The control means14, having already determined the viscosity of the wash fluid, sets afirst wash pressure. It then sends a first pressure command signal 38″to the first wash syringe 30″ to push wash fluid into the fluid path 62.The control means 14 monitors the measured pressure in fluid pathsection 60, and increases the source pressure, until the measuredpressure equals the first wash pressure. This pressure assures that thewash fluid is flowing at the correct rate and assures that thepredetermined volume of first wash fluid is delivered in a timelymanner.

For systems that require two levels of washing, a second controllablepressure source (not shown) functioning as a second wash syringe isfilled with a second wash fluid and connected to port 43″. The firstconnection means 40″ selects between the first and second wash syringes.After washing with the first fluid, the control means 14 uses the firstconnection means 40″ to select the second wash syringe and sends asecond pressure command signal to the second wash syringe until themeasured pressure equals a predetermined second wash pressure. Thecontrol means 14 causes the second wash fluid to flow at the second washpressure until a predetermined volume of second wash fluid has beenprovided.

The device is used in a method of monitoring pressure in a fluid system.In FIG. 2, the fluid system 24 is comprised of at least one fluid pathsection 32 having a first end 36 and a second end 34 and at least onecontrollable pressure source 30 connected to the first end 36 of the atleast one fluid path section 32. Although FIG. 2, does not illustratethis, the connection between the at least one fluid path section 32 andthe at least one controllable pressure source 30 may be through furthercomponents of the fluid system 24. Each controllable pressure source 30is responsive to a pressure command signal 38 to create a sourcepressure in the at least one fluid path section 32. The fluid system 24is connected so that it forms a fluid path filled with a fluid 16. Themethod comprises providing a device 10 comprising a pressure monitor 12for placement in communication with the fluid 16 in a first path section32 and a control means 14. The pressure monitor 12 generates a signalrepresentative 20 of a measured pressure that is received by the controlmeans 14. The control means 14 sends signals 22 to the fluid system 24.The pressure monitor 12 is placed in communication with the fluid 16 inthe fluid path 32. The control means 14 issues a pressure command signal38 to the controllable pressure source 30 to cause it to generate thesource pressure in one fluid path section 32. The control means 14compares the measured pressure to the source pressure, and generates anerror message if the difference between the measured pressure and thesource pressure exceeds a predetermined value.

Preferably, the method determines whether a pressurized system isestablished within a specified time after a source pressure is applied.The fluid system 24 further comprises at least one fluid connectionmeans 40 having a plurality of ports 42, 44, 46, 48 for interconnectingwith the at least one controllable pressure source 30 and the at leastone fluid path section 32. The fluid connection means 40 is capable ofassuming at least a first position wherein fluid flows between at leasttwo of the plurality of ports in response to a connect command signal 52and a second position in which no fluid flows in response to adisconnect command signal 54. A preferred fluid connection means is amultiport valve.

A preferred system, as shown in FIG. 5A, comprises a first fluidconnection means 140 having at least a first port 144 and a second port142, a second fluid connection means 140′ having at least a first port144′ and a second port 142′, a first fluid path section 132 and acontrollable pressure source 130. The controllable pressure source 130is connected to the first port 144 of the first fluid connection means140 and the second port 142 of the first fluid connection means 140 isconnected to a first end 134 of the first fluid path section 132. Thesecond end 136 of the first fluid path section 132 is connected to thefirst port 144′ of the second connection means 140′. The method furthercomprises sending at least one connect command signal 152 to the firstfluid connection means 140 to place the first connection means 140 inthe first, open position wherein fluid can flow between the first andsecond ports 144, 142. And sending at least one disconnect commandsignal 154′ to the second fluid connection means 140′ to place thesecond fluid connection means 140′ in the second, closed, position. Thisarrangement of the fluid connection means 140, 140′ creates a closedsystem that, in the absence of leaks, should maintain an appliedpressure. The control means 14 sends a pressure command signal 138 tothe controllable pressure source 130 to generate a predetermined sourcepressure. The control means 14 compares the measured pressure to thepredetermined source pressure and reports an establishment error if thedifference is greater than a first allowed amount. If no establishmenterror occurs, the method preferably further waits a predetermined lengthof time and compares the current measured pressure to the predeterminedsource pressure again. If the decay in pressure is greater than a secondallowed amount, a leak error is reported.

Further, as fluid systems with more components and potential paths aremonitored, the method above is preferably extended to provide thecontrol means 14 with a library of entries comprising sets of commandsignals, times and sets of normal pressure values. Each set of commandsis sufficient to configure the fluid system. The times are forspecifying the interval between sending the set of commands andcomparing pressures. The control means 14 selects one entry, issues thecommand signals for that entry and compares the measured pressures tothe normal pressure values after the time interval. The control means 14reports significant differences. Preferably, the method has the controlmeans 14 issue connect 152, disconnect 154 and pressure command 138signals to the fluid system and identify degradations in the measuredpressure indicative of reduced fluid integrity.

In particular, after testing the fluid system as depicted in FIG. 5A,the method is preferably applied to a fluid system, shown in FIG. 5B,that is a variation on the tested system. The system comprises a firstfluid path section 132 connected between a second port 144 of a firstfluid connection means and a first port 142 of a second fluid connection140′ means. The device 10 for monitoring measured pressure measures atthe first fluid path 132. A first controllable pressure source 130′ isconnected to the second port 142′ of the second fluid connection means140′. The sequence of steps in the method comprise sending disconnectcommand signals 154 from the control means 14 to the first fluidconnection means 140 to cause it to assume the second position andconnect command signals 152 to the second fluid connection means 140′ toassume a first position in which fluid flows between the first fluidpath 132 and the first controllable pressure source 130′. The controlmeans 14 then sends a pressure command signal 138′ to set the sourcepressure. Finally, the control means monitors the signal from thepressure monitor and identifies non-leaking components based on astability of the measured pressure over time. If the second methodindicates a leaking component, while the first method did not, thecontrol means 14 can suggest that the components common to the twomethods (port 142 of the first fluid connection means 140, the fluidpath section 132 and port 144′ of the second fluid connect ion means)are non-leaking.

The method is adaptable to other configurations. For instance, when asecond controllable pressure source (not shown) is connected to thesecond port of the second fluid connection means, the method has furthersteps. The control means sends at least one connect command signal anddisconnect command signal to the first and second fluid connection meansto place the first fluid connection means 140 in the second position andthe second fluid connection 140′ means in an alternate first position.Now, fluid flows between the first fluid path 132 and the secondcontrollable pressure source (not shown). The control means sends atleast one pressure command signal to the second controllable pressuresource to set the source pressure. The control means monitors the signalfrom the pressure monitor and identifies additional non-leakingcomponents based on the stability of the measured pressure over time.When further controllable pressure sources are connected to a furtherports of the first and second fluid connection means 140, 140′, themethod is extended similarly to identify further non-leaking components.

Preferably, the first fluid connection means comprises aninterconnection of more than one fluid connection means and the secondfluid connection means comprises an interconnection of more than onefluid connection means.

The method is applicable and provides additional information when thecontrollable pressure source providing pressure is located at adifferent fluid connection point in the fluid circuit. In particular,when an additional controllable pressure source is connected to apreviously unused port of a fluid connection means, the control meansconnects the fluid circuit by sending connection command signals to thethat fluid connection means to assume a first position in which fluidflows between the monitored fluid path and the additional controllablepressure source. In addition, the control means sends disconnect commandsignals to some fluid connection means to assume a second positionblocking the fluid path. Then the control means sends a pressure commandsignal to the additional controllable pressure source to pressurize thefluid path. By monitoring the signal from the pressure monitor, thecontrol means identifies additional non-leaking components based on thestability of the measured pressure over time.

Example

A sample injector for a liquid chromatography system is illustrated inFIG. 6A. It comprises an injection mechanism comprised of a needleassembly 278 connected to a multiport valve and a metering syringe 210and a wash mechanism comprising a pair of wash syringes 246, 264, awashing manifold and switching mechanisms 240, 234, 256, 226, and 208 towash the fluid path between injections. A pressure monitor 212 thatfeeds readings to a control means (not shown) monitors the pressurebetween the metering syringe 210 and the multiport valve 200. In testingthe system to identify possible sources source of leaks, a sequence offour tests are performed.

FIG. 6A illustrates the first test. Fluid path 201, from the meteringsyringe 210, through valve means 208 along fluid path section 204, tomultipart valve 200, that is in the disconnect state, is pressurized bythe metering syringe. Because multipart valve 200 is in the disconnectstate, the fluid path 201 is closed and should hold a pressure. If thefluid path 201 does not maintain pressure the failure is likely one of:the metering syringe, pathway 203 through the valve 208 between themetering syringe 210 and the fluid path 204, the fitting 206 at theinterconnection of valve 208 and fluid path 204, the fluid path 204, thefittings 202 between the fluid path 204 or the multipart valve 200 in adisconnect state. If the fluid path 201 maintains pressure, the abovecomponents are likely sealing well and can be used as a basis forfurther tests.

FIG. 6B illustrates a second test path 225 utilizing one of the washsyringes 246 to establish the pressure. This path uses the multipartvalve 200 in the disconnect state, fluid path 204 and the fittings aboveas the known part of the fluid path. The switching mechanisms (valvemeans) 240, 234, 224 and 208, fluid paths 235, 230, 22, and the washsyringe 246 comprise the newly tested parts of the fluid path 225. Ifthis test reveals a leak, the likely leaking components or joints arealong fluid path 225 after the fitting at junction 206 between the fluidpath 204 and the valve 208.

FIGS. 6C and 6D illustrate two further tests that are performed on thesystem illustrated as part of the test sequence. Each of these testsincorporates further components in the fluid path. The test illustratedin FIG. 6C adds the untested components and connections betweenswitching mechanism 226 port 224 and the second washing syringe 264. Inthe test illustrated in FIG. 6D, the needle assembly 278 is inserted ina wash block manifold 276 to allow the fluid path 275 to pass throughthe needle assembly 278. This test requires that valve means 208 at theend of the measured fluid path section 204 seal the fluid path 275 whenin the disconnect position. Further, the valve means 200 is utilized inone of the open positions, with fluid flowing between the ports as shownby connection 286. A further test, would change the position of theinjection valve means 200, so that the seal on the sample loop 294 andthe internal paths 290, 292 to the sample loop 294 were test. Theresults of the four tests illustrated in FIGS. 6A-6D are summarized inFIG. 6E, where most likely failure points are highlighted.

A similar sequence of tests can be constructed for a known fluid systemto minimize the uncertainty of leakage sources.

The numerous teachings of the present application will be described withparticular reference to the presently preferred embodiments. However, itshould be understood that these embodiments provide only a few examplesof the advantageous uses of the teachings herein. In general, statementsmade in the specification of the present application do not necessarilydelimit any of the various claimed inventions. It will be obvious tothose skilled in the art that various modifications can be made withoutdeparting from the spirit and scope of this invention.

What is claimed is:
 1. A method of monitoring pressure in a fluid system comprised of at least one fluid path section having a first end and a second end and at least one controllable pressure source connected to said first end of at least one fluid path section and responsive to a pressure command signal to create a source pressure in said at least one fluid path section, said method comprising: providing a device comprising: a pressure monitor for placement in communication with a fluid in said fluid system, said pressure monitor generating a signal representative of a measured pressure; a control means for receiving said signal representative of said measured pressure and for sending signals to said fluid system; providing said control means with a library having entries comprising sets of command signals and sets of normal pressure values; comparing said measured pressures to said normal pressure values; reporting differences that exceed a preset threshold; placing said pressure monitor in communication with a fluid in said at least one fluid path section; issuing a pressure command signal from said control means to one of said controllable pressure sources to generate said source pressure in said at least one fluid path section; and comparing said measured pressure to a reference said normal pressure values and reporting differences that exceed a preset threshold to identify errors in said fluid system.
 2. The method of claim 1 wherein said fluid system further comprises at least one fluid connection means having a plurality of ports for interconnecting with said at least one controllable pressure source and said at least one fluid path section, said fluid connection means being capable of assuming at least a first position wherein fluid flows between at least two of said plurality of ports in response to a connect command signal and a second position in which no fluid flows in response to a disconnect command signal, said fluid connection means connected to an end of said fluid path section.
 3. The method of claim 2 wherein said fluid connection means is a multiport valve.
 4. The method of claim 2 wherein said fluid system comprises a first fluid connection means having at least a first port and a second port, a second fluid connection means having at least a first port and a second port, and one of said at least one controllable pressure sources is connected to said first port of said first fluid connection means, said second port of said first fluid connection means is connected to a first end of a first fluid path section, a second end of said first fluid path section is connected to a first port of a second connection means, and said method further comprises: sending at least one connect command signal and disconnect command signal to said first and second fluid connection means to place said first connection means in said first position and said second connection means in said second position for creating a closed system; sending a pressure command signal to said controllable pressure source to generate a predetermined source pressure; and comparing said measured pressure to said predetermined source pressure and reporting an establishment error if a difference is greater than a first allowed amount.
 5. The method of claim 4 further comprising after said comparing step: waiting a predetermined length of time; comparing a current measured pressure to said predetermined source pressure: and reporting a leak error if a difference is greater than a second allowed amount.
 6. The method of claim 1 wherein said fluid system further comprises a second controllable pressure source connected to said second port of said second fluid connection means, said method further comprising: sending at least one connect command signal and disconnect command signal from said control means to said first and second fluid connection means to place said first fluid connection means in said second position and said second fluid connection means in said first position in which fluid flows between said first fluid path and said second controllable pressure source; sending at least one said pressure command signal to said second controllable pressure source for setting said source pressure; and monitoring said signal from said pressure monitor and identifying non-leaking components based on a stability of said measured pressure over time.
 7. The method of claim 1 wherein said fluid system comprises a monitored fluid path section having a first end and a second end and a first and second fluid subsystem each fluid subsystem comprising at least one fluid path section having a section first end and a section second end, at least one fluid connection means having a plurality of ports for interconnection and responsive to a connect command signal to assume a first position wherein fluid flows between at least two of said ports and responsive to a disconnect command signal to assume a second position in which fluid does not flow between any of said plurality of ports, at least one port connected to said at least one section first end for forming said fluid subsystem and a controllable pressure source connected to said at least one section second end, said controllable pressure source responsive to a pressure command signal to create a source pressure on fluid in said fluid subsystem, said first fluid subsystem connected to said first end of said monitored fluid path section and said second fluid subsystem connected to said second end of said monitored fluid path section, said pressure monitor in communication with said monitored fluid path section, said method further comprising: sending at least one said connect command signal and disconnect command signal to said second fluid subsystem to create a configuration wherein fluid flows between a controllable pressure source of said second subsystem to said monitored fluid path section; sending at least one said connect command signal and disconnect command signal to said first fluid subsystem to create a configuration wherein fluid does not flow to said first subsystem; sending at least one said pressure command signal to said controllable pressure source of said second subsystem for setting said source pressure; and monitoring said signal from said pressure monitor and identifying non-leaking components based on the stability of said measured pressure over time.
 8. The method of claim 7 further comprising: sending at least one said connect command signal and disconnect command signal to said first fluid subsystem to create a configuration wherein fluid flows between a controllable pressure source of said first subsystem to said monitored fluid path section; sending at least one said connect command signal and disconnect command signal to said second fluid subsystem to create a configuration wherein fluid does not flow to said second subsystem; sending at least one said pressure command signal to said controllable pressure source of said first subsystem for setting said source pressure; and monitoring said signal from said pressure monitor and identifying additional non-leaking components based on the stability of said measured pressure over time.
 9. The method of claim 7 wherein said fluid connection means comprises an interconnection of a plurality of valve means.
 10. The method of claim 1 wherein said fluid system is an autosampler for a liquid chromatography system. 